Dating from the fifteenth century, air guns have been used for war, hunting, and sport. Early guns provided advantages over the match lock powder rifles of the time with improvements in terms of repeatability, quietness, stealth, speed and reliability of fire. However, the limitations on mechanical technology in the fifteenth century made construction of large quantities of reliable air operated guns impractical.
By the mid to late eighteenth century mechanical technology had improved, and air guns were developed for use by European armies. In America in the early part of the nineteenth century Lewis and Clark carried an air rifle with them on their famous exploration of the West.
The operational success of these air guns was largely due to the size of shot used with them. Although the guns provided fairly low muzzle velocities by twenty-first century standards, at most a few hundred feet per second, the shot often used was a lead ball of from about 30 caliber (7.62 mm) to about 60 caliber (15.24 mm) with a weight of a few grams to well over ten grams. As a consequence, some of these air guns had the striking power at 100 yards of a modern day 45 caliber ACP cartridge. Because they often carried a magazine of twenty or more balls and could fire rapidly from their magazines, the air gun gave advantages that were not otherwise available in the nineteenth century. Again, however, mechanical challenges in construction and maintenance limited the use of air guns.
In the eighteenth and early nineteenth century nearly all guns whether powder driven or air driven used spherical balls for ammunition making, in the case of air guns, various mechanisms for loading from a magazine fairly simple to design.
In the modern world the air gun has developed into an ever more effective weapon now usually referred to as a pellet gun which is sometimes operated using gases other than air. Many modern pellet guns are purposely designed to be of relatively low power for reasons of safety and to satisfy legal requirements that have developed around them. However, high power versions of these guns are available, and these can provide muzzle velocities that substantially exceed the speed of sound.
In addition the ammunition for these guns has developed from the lead balls of the past into shapes that are particularly effective when shot through a rifled barrel giving stability to pellet flight. The most popular pellet size is 0.177 inch (4.5 mm) in diameter with a construction that provides a variously shaped head, often, but not always, pointed with a skirt protruding behind a necked down waist. The inside of the skirt is hollow and is designed to expand engaging the rifling of the pellet gun to spin the pellet when the gun is fired. This gives the pellet stability during its flight to the target improving accuracy over round shot.
Calibers other than the 0.177 inch caliber are available with the 0.20 inch (5.0 mm), 0.22 inch (5.5-5.6 mm), and 0.25 inch (6.35 mm) calibers being the most commonly available.
Unfortunately, all of these pellets are quite small to handle with precision. To operate properly the pellets must be oriented in the firing chamber of the pellet gun with the skirt at the back of the chamber so that the expanding gas that fires them can expand the skirt to engage the barrel rifling. The problem has been solved in some pellet gun designs by providing a removable magazine, usually a small plastic ring, loaded with properly oriented pellets that can be forced into the firing chamber by the gun itself.
However, many, if not most, guns are single shot designs. These usually come in two varieties, breech loading and break barrel.
In the breech loading design pellets must be placed on a loading rail in a breech that is about 1 cm long and is usually difficult to reach. This is especially so when a telescopic sight is placed over the breech of the gun. A bolt that is similar to, but smaller than, a bolt action rifle bolt is then used to push the pellet into the chamber of the pellet gun. Each pellet must be loaded by hand, and the small size of the pellets combined with the critical orientation of placement in the chamber of the gun make loading them difficult and often frustrating, the pellets having a proclivity to get reversed or misaligned on the loading rail.
In the break barrel design the barrel and firing chamber of the pellet gun fold away from the rest of the pellet gun, similar to the action found in most double barrel shot guns, and a pellet is pressed into the chamber using a finger to push it home. In this case it is critical to keep the small pellet in proper orientation which is difficult to do because of the pellet's small size compared to the size of the human hand that is loading it into the gun.
A better method of loading pellets into these single shot designs is needed.